Lithography, literally "writing on stone" was discovered in the eighteenth century by Alois Senefelder. Senefelder noticed that a certain kind of stone absorbed both oil and water. He wrote on the stone with a grease crayon and observed that water was absorbed on the non-greasy area. Subsequently, when the rolled the stone in ink, the greasy portion only absorbed the ink. Then by rolling the inked-stone on paper, an image was transferred. (Wolfe, Printing and Litho Inks (6th ed.) p. 299).
Today, the lithographic printing process uses metal sheet which is roughened and sensitized to yield hydrophilic and hydrophobic areas. Lithography is usually reserved for high quality printing, such as advertising and packaging. It is divided basically into two types, heat-set and quick-set. The latter type of ink is applied at ambient temperature and dries by wicking of solvent into the paper.
The lithographic ink users consider that resins for quick-set inks should have the listed qualities:
(1) Magie Oil (aliphatic hydrocarbon) solubility PA1 (2) Fast-drying without energy input PA1 (3) Compatibility with alkyd varnishes PA1 (4) Low odor PA1 (5) Pigment dispersing functionality PA1 (6) Good transfer properties PA1 (7) Anti-skinning, i.e., non-oxidative curing.
Copolymers containing isobornyl methacrylate, one of the preferred monomers of the invention, are shown in various prior disclosures. The following three patents, for example, are assigned to the assignee of the present application. Martorano U.S. Pat. No. 3,940,353 shows a copolymer containing 40 to 60% by weight of isobornyl methacrylate and having an average molecular weight of between 1,000 and 8,500. They are utilized as pigment dispersants and lacquer and in blends with materials such as alkyds, vinyl resins and cellulose ester resins. The materials shown in the examples of that patent are insoluble in aliphatic hydrocarbons, although if styrene is substituted for methyl methacrylate, they possibly could be soluble in certain cases.
Another patent concerned with isobornyl methacrylate is Cenci et al. U.S. Pat. No. 3,485,775. It discloses polymers containing 25-75 parts isobornyl methacrylate and 70-25 parts of methyl methacrylate, which detract from hydrocarbon solubility of the polymer. Small amounts (up to 10% of the weight of the other two monomers) of styrene, ethyl acrylate, or butyl acrylate are permitted. The disclosed molecular weight range of the polymers of this reference is between 10,000 to 2,000,000.
Hurwitz et al. U.S. Pat. No. 3,681,298 discloses polymers having a molecular weight range of 1,000 to 8,500, containing 40-60% isobornyl methacrylate and 40-60% of methyl methacrylate, styrene, s-butyl methacrylate, or n-butyl methacrylate, and up to 5% of an unsaturated acid, and the use of solvents comprising or consisting of paraffins, e.g., octane. Amounts of monomers such as methyl methacrylate for such low molecular weight polymers do not appear to be particularly critical; thus about 50% methyl methacrylate is useful. Pigments are disclosed.
Acrylic copolymers for inks are also known, as shown for example in U.S. Pat. Nos. 3,271,347 (Aronoff et al.) and 3,764,587 (Zunker). The inherent viscosity of the polymer of the latter patent, a measure of molecular weight, is between 0.2 and 0.35 measured at 25.degree. C. using 25 milligrams of polymer in 5 cc of chloroform, which suggests a Mw of 100,000 or greater. The polymer of the Example of Zunker has a calculated T.sub.g of about 43.degree. C. The Aronoff et al. polymer in one embodiment is primarily of vinylidene chloride, with acrylic and methacrylic acid or itaconic acid, with the optional inclusion of other monomers. The vinylidene chloride copolymers have molecular weights in the range of 3,000 to 5,000. Aronoff et al. also mention all-acrylic copolymers, the invention being in the inclusion of polyoxyethylene ethers. No method of preparing the acrylic polymer is disclosed nor are molecular weights. The specific acrylics disclosed have extremely low calculated T.sub.g 's. Aronoff et al. disclose solvents including aliphatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, etc.
U.S. Pat. No. 2,886,549 to Bartl is concerned with aliphatic hydrocarbon (benzine) soluble acrylic polymers for use as lacquers, inks, and textile impregnants. The polymer is solution polymerized at 90.degree. C. and 120.degree. C. which would give a low molecular weight polymer, and molecular weight (not specified) can be controlled with conventional polymerization regulators. The polymers have at least two components, with a third optional component. The first component (50-90 parts) is a cycloalkyl ester of an unsaturated acid such as acrylic acid, methacrylic acid or fumaric acid, etc; the preferred alcohol moiety is, for example, cyclohexanol, mono-, di-, or trimethyl cyclohexanol, or other substituted cyclohexanol. The second component (10-50 parts) is an ester of (meth)acrylic acid with an alcohol of at least eight carbon atoms, preferably 10-18 carbons. The third and optional component (1-20 parts) is a different polymerizable compound such as vinyl acetate, styrene, etc., or one having a reactive aldehyde, epoxy, carboxy, etc. group. Of the examples, Example 1 (80 cyclohexyl methacrylate (CHMA), 20 dodecyl methacrylate (DMA)) gives a polymer with the highest calculated T.sub.g of the examples--just below 30.degree. C. At a theoretical 90 CHMA and 10 DMA ratio, not specifically disclosed, the calculated (not actual) T.sub.g would be about 45.degree. C. As elsewhere herein, unless specified otherwise, the T.sub.g is the calculated value. At an also theoretical 50 CHMA and 50 DMA ratio, this value would be -15.degree. C. Being solution polymerized at high temperatures, the polymer would have a low molecular weight.
A similar disclosure of alkane (ligroine or benzine) soluble acrylic polymers appears in CA. 51, 10925f, mentions a copolymer of 20-40% of a higher alkyl ester such as dodecyl methacrylate or cyclohexyl methacrylate, with styrene and the like. An example is given of a polymer, in parts by weight, of 680 styrene, 320 dodecyl methacrylate, and 200 methyl methacrylate. This would have a calculated T.sub.g of about 36.degree. C. and, because of the polymerization method, a low molecular weight. If it is assumed the polymer is 20 CHMA and 80 styrene, the calculated T.sub.g is about 90.degree. C. whereas with 20 DMA and 80 St the figure is about 50.degree. C. The polymer may be combined with other coating materials such as drying oils, phthalic acid resins, etc.
Another reference of possible interest is U.S. Pat. No. 2,803,611, concerned with an adhesive which contains a blend of a copolymer of lauryl and hexyl methacrylates with limed rosin, a wax-naphthalene condensate and a solvent, particularly a hydrocarbon solvent. These higher methacrylic acid esters give very soft (T.sub.g &lt;-5.degree. C.) polymers.
U.S. Pat. No. 4,005,022 to Vijayendran discloses a liquid toner, for developing electrostatic images, containing (A) 9-99 parts of a saturated aliphatic hydrocarbon havimg a Kauri-butanol number of 25-35, (B) 1-10 parts of an intensifier. The intensifier (B) contains (1) 1-10 parts soap, 80-97 parts aliphatic hydrocarbon, and (3) 3-20 parts of a concentrate. The concentrate (3) contains (a) 8-14 parts pigment, (b) 120-200 parts of an acrylic or other polymer, (c) 180-240 parts saturated hydrocarbon and (d) 0.03-6 parts pigment. The acrylic polymer "Neocryl B-701" mentioned by Vijayendran ("a terpolymer composed of vinyl toluene, i-butyl methacrylate and lauryl or stearyl methacrylate") appears to be similar to the acid-free isobutyl methacrylate-vinyl toluene copolymers of Brown et al. U.S. Pat. No. 3,417,041 (prepared by suspension polymerization using a chain transfer agent to give a low molecular weight). The useful polymers had viscosities in Varsol No. 3 of from 37 to 110 centipoises. Similar waxy polymers made with higher alkyl methacrylates and acids are shown by Finn et al. U.S. Pat. No. 3,532,654 for floor polish emulsions.
Hoshi et al. U.S. Pat. No. 3,912,675 discloses polymers said to have molecular weights of 30,000-300,000 with a T.sub.g of 20.degree.-105.degree. C. in inks using a mixture of an alcohol, an aromatic hydrocarbon, and a glycol ether as a solvent, using a mixture of 5-35 parts acrylic resin with 5-20 parts of a natural resin. An isobutyl methacrylate-acrylic acid copolymer is mentioned. The examples show polymers having intrinsic viscosities of 0.03 and 0.067.